The present application claims priority to Japanese Application No. P2000-059848 filed Mar. 6, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a transportation method for a semiconductor device and a transportation route selection method for a semiconductor device which can prevent the occurrence of defects of a semiconductor device such as a solid state image device due to the transportation route.
2. Description of the Related Art
As one type of image defect in a solid state imaging device (charge coupled device: CCD) there are white defects at the time of a signal for darkness. This is usually separated into two types of modes. That is to say, one is a microscopic defect based on the defect level formed a microscopic amount of impurities, such as a heavy metal, which are mixed in during a process for a semiconductor, which is referred to as initial white defects. Though these initial white defects are the most important problem which affects yield during the manufacturing process, they can be removed before product shipment by carrying out measurement and selection.
On the contrary, the other defect mode are image defects (white defects) which usually occur among the selected good products after the completion assembly, measurement and selection, which are distinguished as white defects occurring after production. The white defects occurring after production exist among products shipped as good products and, therefore, this occurrence of defects is very critical which directly relates to the defects in all products into which a solid state imaging device has been built in.
As for the causes of the occurrence of the white defects occurring after production of a solid state imaging device, xcex1 rays in the packaging material or extrinsic cosmic rays are known. As for the xcex1 rays in the packaging material, measures are implemented by introducing materials in which the xcex1 ray concentration is as low as possible with respect to the materials utilized for a variety of packaging materials or during the wafer process.
For example, in the case where sealing glass used as a package for a solid state imaging device includes a radioactive element, such as uranium (U) or thorium (Th), the uranium (U) or the thorium (Th) xcex1 decay so as to generate xcex1 rays. When these xcex1 rays enter the solid state imaging device, the energy loss process thereof is divided into electronic energy loss and nuclear energy loss.
In the electronic energy loss process hole and electron pairs occur and, in the case of a solid state imaging device, this charge generates a spike of a customary dark current from pixels. And, in the case of a semiconductor memory, this charge due to the electronic energy loss causes a malfunction of the memory. This phenomenon is a so-called soft error.
And, in the nuclear energy loss, crystal defects of silicon occur, so that these crystal defects are fixed while generating a defect level in the silicon, and become permanent flaws. In the case of a solid state imaging device, the dark current in the pixels and transferring parts are increased.
With respect to white defects of a solid state imaging device, in the same manner as xcex1 rays, cosmic rays also cause defects. The amount of cosmic rays differs according to altitude and the higher the altitude is, the stronger the cosmic ray intensity becomes. For example, the cosmic ray concentration becomes 100 times, or more, as high as that on the ground in the vicinity of 10,000 m, which is an aircraft flight altitude. Therefore, the white defects of a solid state imaging device caused by exposure to cosmic rays during flight have become a critical issue.
In addition, the cosmic ray intensity differs according to the longitude of the location and that intensity distribution is similar to the distribution of the horizontal component of the geomagnetic force and is larger by one order, or more, in the polar regions than in the vicinity of the equator. Accordingly, in the case that a solid state imaging device is transported from Japan to Europe or to the U.S.A., a direct flight passing through the vicinity of the Arctic Circle has the problem that the effects of cosmic rays are significant because the flight passes through a region where the cosmic ray intensity is strong.
These cosmic rays are attenuated by passing them through a substance. However, the energy of the cosmic rays is of a high energy, with a unit of GeV, and is scarcely attenuated through a conventional package for transportation (cardboard boxes, thin duralumin trunks, or the like) which cannot be expected to have an effect against white defect occurrence.
The present invention is provided so as to solve such a problem. That is to say, the present invention is a transportation method for a semiconductor device which uses a transportation route where the cosmic ray concentration is the smallest among a plurality of transportation routes from a departure point to an arrival point at the time when a semiconductor device is transported from the departure point to the arrival point.
In addition, the present invention is also a transportation route selection method for a semiconductor device comprising the step of inputting a departure point and an arrival point for the transportation of a semiconductor device, the step of calculating a plurality of transportation routes from the departure point to the arrival point, the step of calculating the cosmic ray concentration in each of the plurality of transportation routes and the step of selecting the transportation route where the cosmic ray concentration is the smallest among the plurality of transportation routes.
In the present invention configured as above, since the transportation route where the cosmic ray concentration is the smallest is selected from among transportation routes for a semiconductor device, the amount of exposure to the cosmic rays during the transportation of a semiconductor device can be restricted to the minimum so that the white defects which used to occur at the time of transportation can be reduced to a great extent.